Stator vanes are commonly used in gas turbine engines to control the aerodynamic characteristics of the compressor blades and, as a result, compressor flow and compressor stage pressure drop. A major use for stator vanes is in controlling compressor stall.
A typical stator vane control is mainly a mechanical system with linkages and arms to change the orientation of stator vanes in the airflow path to the compressor blades. U.S. Pat. No. 4,995,786 is representative of a stator control in use on gas turbine engines. An unavoidable limitation with these systems is imprecision in controlling stator vane angle or deflection (SVA) resulting from manufacturing tolerances, hysteresis and other inaccuracies in the stator control path. This has an impact on engine design, particularly high performance aircraft engines. Those losses produce "slop" in the control path between the stator vane control input and the stator vanes. An effect is that the compressor does not necessarily operate with optimum flow at a particular compressor speed; the flow may surge with small shifts in vane deflection caused by those control path losses. To compensate for this, the compressor can be designed with extra surge margin for a worse case condition, just in case the SVA is not what it should be when peak power is suddenly demanded. But, this over design limits peak performance, especially during rapid acceleration and deceleration.